Surface fluorinated hydrogen containing material and process for making

ABSTRACT

A MANUFACTURED MATERIAL AND A PROCESS FOR MAKING THE MATERIAL IS DISCLOSED. THE MANUFACTURED MATERIAL IS A HYDROGEN CONTAINING SUBSTANCE HAVING A FLUORINATED SURFACE AND IN WHICH HYDROGEN ATOMS, WHICH MAY BE PRESENT IN HYDROXYL RADICALS ATTACHED TO A CARBON ATOM CHAIN, HAVE BEEN REPLACED IN THE SURFACE OF THE MATERIAL BY FLUORINE ATOMS OR RADICALS, AND WITH SUCH FLUORINATED SURFACE OF THE MATERIAL CONTAINING AT LEAST ABOUT 2 MICROGRAMS OF SUCH FLUORINE PER CM.2 OF SURFACE AREA. THE PROCESS FOR MAKING SUCH A MATERIAL INCLUDES THE STEPS OF SELECTING A SUBSTRATE CONTAINING HYDROGEN ATOMS WHICH MAY BE PRESENT IN HYDROXYL RADICALS ATTACHED TO A CARBON ATOM CHAIN, SELECTING A GAS CONTAINING FLUORINE ATOMS OR RADICALS, PLACING THE SELECTED SUBSTRATE BETWEEN ELECTRODES IN A FLOWING ATMOSPHERE OF THE SELECTED GAS AT SUBATMOSPHERIC PRESSURE, AND SUBJECTING THE SUBSTRATE TO AN ELECTROLESS DISCHARGE OF AT LEAST ABOUT 0.2 KWH./YARD2 TO CHEMI-   CALLY ACTIVATE BOTH THE SURFACE OF THE SUBSTRATE AND THE GAS, AND EXCHANGE THE FLUORINE ATOMS OR RADICALS FOR SURFACE HYDROGEN ATOMS OR RADICALS TO PRODUCE A MATERIAL WITH A SURFACE, WHICH COMPARED TO THE SUBSTRATE BEFORE THIS PROCESS TREATMENT, IS MORE WATER REPELLENT (WITHOUT SEALING PORES), IS MORE CORROSION AND SOIL RESISTANT, MORE CHEMICALLY INERT, AND MORE LIKE THE RELATIVELY EXPENSIVE POLYTETRAFLUOROETHYLENE. WHEN THE SUBSTRATE IS A MATERIAL HAVING A RELATIVELY INERT SURFACE, SUCH AS POLYETHYLENE, THE PROCESS IS DISCLOSED AS INCLUDING AN INITIAL TREATMENT STEP THAT INVOLVES ION BOMBARDMENT OF THE SUBSTRATE IN HELIUM GAS TO ACTIVATE THE SURFACE BEFORE THE SURFACE IS TREATED IN THE FLUORINE CONTAINING GAS.

June 19, 1913 6A5 INLET me SEAL as 33 meme or: MATERIAL 10 BE TREATED 37J. P. MANION ET SURFACE FLUORINATED HYDROGEN CONTAINING- MATERIAL ANDPROCESS FOR MAKING Original Filed Aug. 1, 1969 2 Sheets-Sheetl 3| gTANTALUM WIRE SPIRAL ELECTRODE 40 IN PLANE PERPENDICUAR TO CELL AXIS 2Sheets-Sheet 2 QDISCHARGED TREATED 2A SURFACE ARE W. C... m a m U EPROCESS FOR MAKING J. P. MANION ET AL SURFACE FLUORINATED HYDROGENCONTAINING 4 MATERIAL AND Original Filed Aug. 1, 1969OTREATEDPOLYETHYLENE 2 a 4- 5 5 mosuns TIME (HOURS) AT 75c 5/0 4UNTREATED POLYETHYLENE $256.33 $3 Ewm June19, 1973 ZEOQE United StatesPatent SURFACE FLUORINATED HYDROGEN CONTAHI- ING MATERIAL AND PROCESSFOR MAKING Jean ll. Manion, Milwaukee, and Daniel Ii. Davies,

Mukwonago, Wis., assignors to Allis-Chalmers Manufacturing Company,Milwaukee, Wis.

Original application Aug. 1, 1969, Ser. No. 846,767, new Patent No.3,674,667. Divided and this application Sept. 22, 1971, Ser. No. 188,671

Int. Cl. C23c 11/00 US. Cl. 117-931 CD 2 Claims ABSTRACT OF THEDISCLOSURE A manufactured material and a process for making the materialis disclosed. The manufactured material is a hydrogen containingsubstance having a fluorinated surface and in which hydrogen atoms,which may be present in hydroxyl radicals attached to a carbon atomchain, have been replaced in the surface of the material by fluorineatoms or radicals, and with such fluorinated surface of the materialcontaining at least about 2 micrograms of such fluorine per cm. ofsurface area. The process for making such a material includes the stepsof selecting a substrate containing hydrogen atoms which may be presentin hydroxyl radicals attached to a carbon atom chain, selecting a gascontaining fluorine atoms or radicals, placing the selected substratebetween electrodes in a flowing atmosphere of the selected gas atsubatmospheric pressure, and subjecting the substrate to an electrolessdischarge of at least about 0.2 kwh./yard to chemically activate boththe surface of the substrate and the gas, and exchange the fluorineatoms or radicals for surface hydrogen atoms or radicals to produce amaterial with a surface, which compared to the substrate before thisprocess treatment, is more Water repellent (without sealing pores), ismore corrosion and soil resistant, more chemically inert, and more likethe relatively expensive polytetrafluoroethylene. When the substrate isa material having a relatively inert surface, such as polyethylene, theprocess is disclosed as including an initial treatment step thatinvolves ion bombardment of the substrate in helium gas to activate thesurface before the surface is treated in the fluorine containing gas.

This is a division of application Ser. No. 846,767, filed Aug. 1, 1969now Pat. No. 3,674,667.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a product and a process for making the product, utilizing anelectrical discharge to improve certain desired surface characteristicsof certain nonmetallic materials and in particular for improving thewater repellency of textiles and paper materials and corrosionresistance of polymeric materials; while maintaining unchanged suchcharacteristics of the bulk of the material as the mechanical strength,the dielectric strength, and the resistance to thermal degradation. Thefield to which the present invention relates therefore encompassestreatments for providing a material with a combination of properties,i.e. properties associated with the surface and properties associatedwith the bulk of the material, not characteristic of the material beforetreatment.

Description of the prior art Although a Wide variety of polymericmaterials are available, both natural and synthetic, the desiredcombination of properties (at least at prices required for practicalcommercial applications) is frequently not found in any one material.Formulations involving mixtures of compati- 3,740,256 Patented June 19,1973 ble material with filler are frequently resorted to but with onlylimited success.

For'the special need for materials having such as the previouslymentioned desired surface properties combined with desired propertiescharacteristic of the bulk of the material, graft polymerization hasbeen used to apply a surface graft having the desired surfaceproperties, on to a base of a polymeric material having other desiredproperties. According to the prior art this may be accomplished ineither of two ways. One way is to activate a polymer surface with highenergy radiation or an RF discharge in the presence of an eligiblemonomer as described in US. Pat. No. 3,068,510 to Coleman. A secondapproach known to the prior art involves the use of a polymer made underconditions which preserve an active site for the later graft reaction.In the first approach the radiation level required for significantsurface treatment results in excessive cross-linking of the basematerial and subsequent loss of desirable bulk properties. The secondapproach is limited in application to special systems such ascondensation polymers} 2 Graft polymerization, by whatever prior artapproach it is achieved, involves a disadvantage when applied for thepurpose of making such as a tenting material or wearing apparel waterrepellent. The disadvantage of graft polymerization is a result ofcomplete surface sealing, including pores, which eliminates the propertyof air breathing so important to providing a comfortable rain repellentapparel or tenting material.

It is also known to the prior art that surfaces of natural and syntheticfibers (woven or nonwoven) may be treated with an electrical dischargein certain gaseous mediums to provide increased adhesion and wettingproperties im portant to providing a surface which, for example, adheresto other materials or provides improved ink and dye retention,resistance to corona degradation, slip and antistatic properties.Adhesion, however, is a characteristic that may be viewed as being theopposite of water repellency. The gases used in these prior artpractices to increase adhesive properties are inoperative to increasewater repellency and corrosion resistance of materials so treated, whichis sought and achieved, as will be later explained, by the presentinvention. Certain US. patents may be identified which are examples ofthis prior art approach (i.e., treating a surface to increase itsadhereability and wettability rather than applying a graft by either ofthe heretofore described graft approaches). For example, the prior artdescribed in US. Pat. No. 3,291,712 to McBride discloses thatperfluorocarbon polymers are very resistant to corrosion and the actionof most chemicals and solvents. The McBride patent further states thatperfluorocarbon polymers are therefore used to line pipes and vesselsused to transport or store chemicals but that perfluorocarbon polymersdo not adhere well to such surfaces. This McBride patent also disclosestreating the surface of a perfluorocarbon polymer web with an electricaldischarge in the presence of an amine vapor to render theperfluorocarbon web strongly adhereable to other materials so it can beeasily applied to and will adhere well to pipes, vessels and the like.

Another example of a prior art patent related to treatingpolymeric-shaped structures to increase their adhereability to othermaterials and their wettability by other materials (i.e., ink, dye,etc.), US. Pat. No. 3,255,099 to Wolinski. This Wolinski patentdiscloses achieving such objects by treating polymeric-shaped structureswith an electrical discharge in the presence of a vapor of an inorganicagent having an affinity for electrons.

1 Atomic Radiation and Polymers, A. Charlesby, Pergamon Press (1960), p.498 et seq.

Chapiro, A. J. Polymer Set 23, 377 (1957).

Still another example of a prior art patent related to treatingpolymeric-shaped structures to improve its adhereability and in thiscase also its heat scalability, is another U.S. patent to Wolinski No.3,255,089. This Wolinski patent discloses treating the surface ofpolymeric-shaped structures with an electrical discharge in the presenceof an organic compound selected from the group consisting ofpolymerizable organic compounds, nonpolymerizable compounds havingreplaceable hydrogen atoms, and perhalohydrocarbons having a bonddisassociation energy for the carbon halogen bond below 100kilocalories. The stipflulation that perhalohydrocarbons having acarbonhalogen bond below 100 kilocalories, in order to be within thescope of Wolinskis teachings, makes it completely clear to those skilledin this art, among whom the present inventors number themselves, thatthe Wolinski teaching excludes fluorine-containing perhalohydrocarbonssuch as are involved in the present invention, in different mechanismsand for different purposes, as will appear from the description tofollow.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide new and improved materials by a process for upgrading the valueof certain low cost materials to thus providing new and more usefulmaterials, by treating the surface thereof to impart properties to thesurface that are equal to or superior to properties of relatively highcost materials.

Another object of the present invention is to provide an inexpensiveprocess for upgrading the value of certain already relatively expensivematerials by treating the surface thereof to further improve desiredsurface properties that are already possessed by and characteristic ofsuch materials, and thereby increase the economic justification forusing such expensive materials.

More specific objects of the present invention include providing aprocess for treating materials to improve the surface properties such aswater repellency to make such materials more useful and comfortable forsuch as tenting and rain repelling apparel; and for treating materialsto improve surface properties such as corrosion resistance to make suchmaterials more useful for such as coating or wrapping Wires and cablesfor underground burial.

These and other objects that are achieved in a manner that will bedescribed, involve attaining goals are the exact opposite of increasingadhereability, wettability, etc. which are the goals of the describedprior art. It is in the nature of a discovery by the present inventorsthat the achievement of the objects of this invention requires amaterial to be treated which has in its surface hydrogen atoms which maybe present in hydroxyl groups attached to a carbon atom chain, and atreating gas containing fluorine atoms or fluorine containing radicals.As will appear as the description of this invention proceeds, thisinvention does not involve graft polymerization (e.g., Coleman) nor doesthis invention involve treating a surface to make it more adhereable toother materials (e.g., Wolinski). This invention does, however, involvean electrical discharge being utilized to chemically activate both asurface containing hydrogen atoms or hydrogen radicals and a treatinggas containing fluorine atoms or fluorine radicals (with gaseousperfluoro compounds proving most satisfactory) resulting in an exchangeof the fluorine atoms or radical for the hydrogen atom or radical, andthe product-ion of a surface that is more water repellent (withoutsealing pores), more corrosion and soil resistant, more chemically-inertand more like the realtively expensive polytetrafiuoroethylene which isknown by the Du Pont trademark Teflon, than was the surface before suchtreatment.

Materials which can be used as a substrate to be treated by the presentinvention, and which possess hydrogen atoms with or without hydroxylradicals, attached to a carbon chain molecule include su h as OttOn,Wool,

rayon, paper and the cellulosic polymers, polyethylene, polyproplylene,and the polyolefins, nylon, Dacron, Orlon (Dacron and Orlon are Du Ponttrademarks), and the polyesters, polyvinyl fluoride and the polyvinyland polyacrylic polymers, epoxy, phenol, formaldehyde, polyurethane, anda great many other such materials.

Treating gases containing fluorine atoms or radicals, operative with thepresent invention include the following perfluoro compounds CF C F C F CF CHF and SP For treating some materials, for example polyethylene, apreferred process according to the present invention amy include apretreatment in helium gas to cleanup and activate the polyethylenesurface for better treatment thereafter by the fluorine atom containinggas.

TESTS AND MEASUREMENTS In the description of the invention to followmany examples will be described and evaluated relative to each other andcontrol (untreated) samples of the same materials treated according tothis invention. In order to present such evaluations certain tests andmeasurements were used which will now be described.

Water repellency Two tests for water repellency were used. One test wasa static water drop test. This test consisted of placing drops ofdistilled water on a fabric surface to be treated using a spacing ofapproximately one drop per square inch. Delivery of the drops to thefabric surface was from a standard pipette to assure reasonablereproducibility of size. Water repellency rating was taken to be thetime after drop addition to the first sign of fabric wetting,penetration or wic-king for any drop. The untreated control samples ofcotton or paper tested absorbed a water drop completely in 1-3 seconds.The un treated control samples of synthetic cloths absorbed the dropcompletely in l5 minutes. Typically, a cloth, natural or synthetic, orpaper, treated according to the present invention, maintained 28 dropsfor 24 hours (a 28 square inch sample was usually tested).

A second test conducted for water repellency was the AST M D-583-63static immersion test (1968 Book of ASTM StandardsPart 24-TextileMaterials, American Society for Testing and Materials, Philadelphia,Pa.). The samples, after conditioning at a relative humidity of 65%,were weighed, immersed in water at an average hydrostatic head of 3.5inches for 20 minutes at ambient temperature. The samples were thenplaced between two pieces of dry blotting paper and passed through awringer having a constant load to remove interstitial water andreweighed. The percentage Weight gain is taken to be due to the waterabsorbed.

Tensile strength Tensile strength of both dry and wet kraft paper wasmeasured. One-half inch strips, 5 mils thick and eight inches in lengthwere cut from treated paper and from untreated paper and the tensilestrengths measured with an Instron Model 'IT-C Universal Testingapparatus. The use of a liquid immersion test attachment permitted wetstren th tests to be performed with the water level several inches abovethe upper Instron jaw.

Fluorine analysis Polyethylene film, cotton cloth and kraft papersamples were analyzed for fluoride content using a micromethod ofYamamura et al. (Analytical Chemistry, volume 34, p. 1308 of 1962) withminor modifications. Lanthanum nitrate was substituted for ceriumnitrate, the complexing agent. It was also necessary to ignite thesamples wrapped in a platinum screen in an oxygen-filled, taped, quartzflask containing water to obtain the fluoride in watersoluble form. Themethod, as modified, was calibrated with known samples prepared from astandard sodium fluoride stock solution.

Corrosion measurements The resistance of treated polyethylene surfacesto accelerated oxidative attack was determined by the immersion oftreated samples according to the present invention in concentratedanhydrous chromic acid solution (150 milliliters conc. H SO /40 grams ofNa 'Cr O at 75 C. and measuring their weight loss. Treated samples,together with an untreated control sample of polyethylene and a similarsample of polytetrafluoroethylene were oven-dried and weighed before andafter various times of acid contact.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic illustrationof an apparatus operative to demonstrate the present invention;

FIG. 2 is a side view of the electrode arrangement in apparatus shown inFIG. 1;

FIG. 3 is a diagrammatic illustration of an early model of a batchapparatus operative to practice the present invention;

FIG. 4 is a graph depicting corrosion resistance of materials;

FIG. 5 is a graph depicting fluorine content in the surface ofmaterials; and

FIG. 6 is a graph depicting the effect of exposure time of a material toa treatment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, adevice for practicing and demonstrating the present invention includes achamber 1 containing a supply roll 2 and a takeup roll 3 with a span ofsubstrate material 4 extending therebetween through an inner chamber 5.The inner chamber 5 is provided with guide slits 6, 7 aligned toposition a midportion of span 4 between an upper array of electrodes 8and a lower array of electrodes 9. The electrodes 8, 9 are supported attheir end portions by support walls 10, 11. Suitable means (not shown)may be applied to roll 3 to rotate roll 3 and draw material through theinner chamber 5. The inner chamber 5 is also provided with an evacuationport 12 for connection to a standard pump (not shown) such as a WelchModel 1397. The chamber 5 is also provided with a treatment gas inlet 14for connection to gas supply sources (not shown). As shown in FIG. 2,the support walls 10, 11 are provided with gas flow holes 18 in wallbelow the span of material 4 and gas flow holes 19 above span 4 in wall11. Gas admitted at 14 thus passes over and beneath the material 4before being drawn out at 12. The gases used in the examples which willbe described, were of commercial grades of CR; (95-98%); CHF (98%); C 'F(99.6%); C4F CClgFg SP6 N3 (98%) and helium (99.99%) produced by theMatheson Company Inc., and such gases with no further purification wereused at the selected pressure, measured at a port 16 at extremely lowflow rates, e.g., 5 millimoles of gas per minute.

Each electrode comprises a glass or metal tube 20, which may be forexample a tube of borosilicate glass of 6 mm. outside diameter, andcontains a filament 21 which may be a wire, a roll of metal foil or anelectroplated metallic deposit on the inner surface of the tube. Eachelectrode of the upper electrode array 8 is connected electrically inparallel as were the electrodes of the lower array 9. Power wasconnected at electrodes 8a and 9a. The power source used (not shown) wasa Lepel Model T-2.51KC-MS high frequency induction heating unit whichwas modified to drive an air core, high frequency transformer for theproduction of high voltage in the 200 to 500 kc. frequency range.Electrical power dissipated in the chamber 1 was determined with aTetronix oscilloscope, Model 536, equipped with an electronic switch.Discharge voltage and current were observed simultaneously and the phaseangle and frequency measured.

Because the filament 21 is within such as a glass tube, the discharge issuch as is known to those skilled in related arts as an electrodelessdischarge.

Referring to FIG. 3, an apparatus is shown that is an early model of abatch apparatus used to treat materials in tubular form. This apparatushas a cylindrical cell 30 with a gas port 31 and a gas outlet port 32for connection to a vacuum system (not shown). Openings 33, 34 areprovided in cell 30 perpendicular to the gas inlet port 31 and gasoutlet port 32. A metal electrode 35 is arranged within a closed endglass insulation tube 36 which projects through opening 33 into cell 30.A tubular sample 37 of material to be treated is arranged over the glasstube 36 to be centrally located within cell 30. A ring seal 38 isprovided to prevent treatment gas escaping around the periphery of tube36. A tantalum wire spiral electrode 40 projects through opening 34 andis arranged to present the plane of the spiral 41 perpendicular to acentral axis through cylindrical cell 30. The Wire electrode 40 is drawnthrough a seal 42 inserted in opening 34. The power source .is a CencoTesla Coil, catalog number 807 00, driven by a 15 kv., 60 milliampereneon sign transformer and spark gap. Maximum primary circuit power was50 watts. Although load output was not determined, the knowninefficiency of this power unit accounts for the time required foreffective treatment of polyethylene. As will be shown, treatment timeand treatment power are inversely related. Treatment time can be reducedwith increase in power and more efficient use of the power supplied thanwas possible with the Tesla unit used.

The present invention as practiced with either the apparatus of FIGS. 1,2 or 'FIG. 3, provides a general polymer surface treatment techniquewhich renders polymer film and solid surfaces (as opposed to porous orwoven) more chemically-inert like Teflon and which produces an equallychemically-inert surface on porous fibers, porous paper, wood and woventextiles, natural and synthetic, rendering them water repellent withoutchange in their porosity or air-breathing characteristics.

In general, surface treatment of the material to be treated, isaccomplished by subjecting the material to an electrodeless discharge inan atmosphere of gas within chamber, in which the gas molecules containfluorine atoms. As will appear from the description of examples tofollow gaseous perfluorohydrocarbons have been found to yield the bestresults with respect to treatment efficiency and absolute treatmentachieved.

With the apparatus of FIG. 1, woven textile, polymer or paper sheets aredrawn through slit 6, between the upper and lower electrode arrays 8, 9in chamber 5 and through slit 7 to take-up roll 3. The verticalseparation between the upper and lower electrode arrays 8, 9 has beenvaried and a separation of 0.5 inch between upper and lower electrodecenters has been used to advantage with 6 mm. O.D. glass tube electrodesarranged in the arrays 8, 9. As stated previously, each glass tubecontains a conducting filament 21 and the upper electrodes 8 areconnected electrically in parallel as are the lower electrodes 9. Anadvantage for the electrode array shown in FIG. 1 is that both sides ofthe span 4 of film, paper or textile fabric are treated equally and, ofcourse, simultaneously.

PROCESS VARIABLES Gas flow rates and condition At the discharge wattagesused the lowest gas flow rates measured were found to yield adequateexchange and in examples to be described, was approximately 5 millimolesof CF; per minute at a pressure of 5 torr. For continuous operation overextended periods a small recycle pump (not shown) preceded by a chemicalabsorption chamber (not shown) may be used. The chemical absorptionchamber can contain an alkaline substance such as sodium hydroxide orother alkaline material having low vapor pressure to react with thehydrofluoric acid and is followed by a section of drying agent such as8-14 mesh activated alumina to insure the treatment gas being returnedto the treatment chamber 1 as dry as possible. As will be shown later,the efficiency of paper treatment is decreased significantly by thepresence of residual moisture in the paper.

Gas pressures The required pressure of the treatment gas has been foundto vary with the type of surface being treated. Thus, althoughacceptable treatment of the textile fabrics, natural and synthetic, areobtained over a Wide range of subatmospheric pressure, optimizedtreatment occurs over a moderately narrow pressure range around torr,that is, between about 0.5 and 50 torr. In the treatment of kraft papereffective treatment is achieved at pressures over the range 0.5 to 400torr. In general it has been found that the pressure range in whichtreatment is optimized is related to the discharge voltage, sinusoidalor pulsed, as the case may be. Optimized pressure is proportional tovoltage measured on load. In this connection, a pulsed voltage has beenfound desirable for film surface treatment with pulse voltage on loadexceeding 20,000 volts, while a sinusoidal voltage performssatisfactorily for treatment of the porous and woven fabric materialswith load voltages of 1000 to 3000 volts proving adequate and it will benoted 2600 volts were utilized for Examples 4-8, Table II.

Power applied (and its relationship to treatment time) Series A Examples1-3 A series A of Examples 1-3, set forth in Table I, show thattreatment time and discharge power are inversely proportional. For eachof these examples the flow rate of the treatment gas was 5.4 millimolesof CE, per minute at a pressure of 5 torr. The apparatus of FIG. 1 wasused. The treatment times used in most examples are determined primarilyby the characteristics and capabilities of the electrical power suppliesused. The energy required per unit of surface treated to the presentoptimized state has been found to be within the accuracy of themeasurement 0.2 k.w.h./yard for a variety of surfaces studied includingcotton, wool, paper and the synthetic fabrics. Examples shown in TableIV applied 0.2 k.w.h./ yard and it will be noted that Example 14achieved a water repellency test substantially better (i.e. 20.8%) thanis shown in the following Table I which reports examples utilizing onlyabout 0.07 k.w.h./yard TAB LE I immersion test, percent Power ExampleNo.

Treatment time Series B Examples 4-8 In a series B of Examples 4- 8involving treatment times of from 25 to 400 seconds a span 4 of cloth tobe treated with the apparatus of FIG. 1 (bleached and desized 80 x 80Weave cotton) was wound on the supply roll 2 and the end threadedthrough the guide slits 6, 7 and between the upper electrode array 8 andthe lower electrode array 9 and attached to the take-up roll 3. (Aseries F of Examples 54'91 described later, will involve treatment timesas short as 3 seconds.)

The treatment chamber 1 was sealed and evacuated via outlet port 12using a Welch Model 1397 mechanical pump. After evacuation to belowmillitorr absolute the electrical terminals 21 of the electrodes 8a and9a were connected to the described source of high voltage continuouswave radio frequency power. For the series B Examples 4-'8, CF gas wasadmitted to the chamber via the inlet port 14 and its flow directed overand under the cloth via the gas flow holes 18, 19 (FIG. 2) in theelectrode support panels 10, 11.

The CE; gas pressure was read on a gauge connected to pressure gaugeport 16 and adjusted by means of throttling outlet port 12 to thepressure of 5 torr after setting the flow rate at the valve of the gassupply cylinder (not shown) to a value of 5.4 millimoles/min.

The area of cloth to be treated was moved into the space betweenelectrode arrays 8 and 9, and the electrodes were subjected to anelectrodeless discharge of 585 watts peak power at 2600 volts peak topeak measured at reaction chamber terminals 21, for the length of timeindicated in the following Table II. Table II shows how in thetreatments of Examples 4-8, series B, the amount of water absorbed wasreduced compared to an untreated control sample of the same cotton clothand the effect of treatment times on the results obtained.

Pretreatment wash Series C Examples 9-13 The materials used for Examples913 were samples of the same bleached and desized -80 weave cotton clothused for series B Examples 4-8. In Examples 9l3 the samples were firstthoroughly washed in distilled water to remove residual chemicals fromdesizing after which the same steps were followed in the treatmentprocessing and testing as for series B Examples 4-8. The following TableIII shows how inclusion of a washing step in the treatment processing ofseries C examples made the material even more water repellent than thetreatment processing of series B as shown in Table II and loweredconsiderably the length of treatment required to achieve a given degreeof water repellency as measured by the immersion test.

TAB LE III Water repellency (static Series 0 Treatment immersion ExampleNo. time, sec. test), percent 25 40.0 50 27. E 19. 4 200 18. 8 400 19. 0Control 56. 8

Nature of the treatment gases Series D Examples 14-49 ment processesExamples 14-49 the treated cotton samples were tested for waterrepellency using the water drop test. After treatment processes with 100second treatments, i.e. Examples 14, 18, 22, 26 and 30, the treatedcotton samples were also tested for water repellency using the staticimmersion test. For each of these Examples 14-49 the results shown inthe following Table IV demonstrate that optimized treatment is (a)restricted to the perfluorocarbon gases, i.e. perhalohydrocarbons havingthe CX bond greater than 100 kilocalories (where X=halogen), (b) thepresence of hydrogen in a treatment gas molecule decreases significantlythe efficiency of surface treatment achieved, (c) the presence ofchlorine results not only in a decrease in efliciency (longer treatmenttime required) but in a significant decrease in the maximum amount ofwater repellency which could be obtained for any treatment time used and(d) the use of N 0, an oxidizing agent and electron receptor resulted inno treatment as measured by the water repellency tests.

TAB LE IV TABLE V Voltage Water Treat- (max. repellency ment peak tostatic Example time peak Power immersion 5 number Fabric (sec.) volts)(watts) test, percent 5 Cotton 50 2,600 585 43.1 Contro1 Untreated 56.8

cotton. 50 Rayon 50 2,400 405 20.0 Control Untreated 32. 8 10 rayon.

5 Nylon 50 2, 700 610 10. 8 Control-.. Untreated 14.6

nylon 6 Cotton 100 2,600 585 27.0 Contro1 Untreated 56.8

cotton. 52 Wool 100 2,600 310 21. 3 00mm"... Untreated 45.8

wool. 53 Dacron 100 2, 700 560 14. 3 Control Untreated 19. 3

Dacron.

Water repellency Water repelleney water drop test in hours (staticimmersion (Control=13 seconds) test, percent Treatment time (seconds)Series D Control=56.8%) Example No. Gas 100 see. 100 sec. 50 sec. sec.10 sec CF 20. 7. 75 7. 75 7. 50 3. 75 24. 0 8. 25 7. 50 8. 25 2. 00 26.0 8. 25 8. 25 8. 25 3. 50 29. O 8. 00 6. O0 4. 25 0. 50 25. 0 8. 00 2.50 0. 05 0. 25 0. 0. 08 0. 07 0. 05 O. 12 0. 08 0. 03 0. 02 0. 17 0.050. 03 0. 03 0. 00 0. 00 0. 00 0. 0O

As appears from examples described, treatment gases are those containingthe fluorine atom, with perfluoro compounds such as CF C F C F C F andSP the most satisfactory. The presence of hydrogen as in CHF in thetreatment gas results in decreased efliciency and the presence ofchlorine as in CCl F reduces the amount of treatment achieved to almostnegligible amounts. Gases such as tetrafluorethylene,hexafl'uoropropylene, are conceived as being good treatment gases.However, because of their unsaturation, polymerization as well aschemical replacement occurs and the polymerization reactionpredominates. Fabrics treated in an atmosphere of 0 E, quickly losetheir hand and suffer loss of their airbreathing property. Similarly,reagents such as BF and SiF are conceived as being good treatment gases.However, because of their rapid chemical reaction with even traces ofmoisture to yield the white powdered products, H BO and H SiOrespectively, their use in a process requiring frequent opening of thereactor would result in contamination of the reactor and of treatedporous materials with the H BO or H SiO and HF produced in theirreaction with the moisture in the air.

Materials treated-textile fabrics other than cotton Series E Examples-53 Examples 1-49 all involve cotton and Examples 50-53 of series E,involve treating a variety of textile fabrics other than cotton,according to the present invention. For these examples the treatment was0P at a pressure of 5.0 torr and with a flow rate of 5. 4 millimoles fortreatment times of 50 and 100 seconds as indicated in Table V, whichwere also the conditions for the cotton Examples 5 and 6 of series B setforth in Table II. In the following Table V the Examples 5 and 6 arerepeated for conven ience in comparing with cotton the examplesprocessing wool, rayon, nylon and Dacron.

It is seen in the data of Table V th'at significant improvements inwater repellency are obtained for all fabrics treated and that evennylon, which is relatively water repellent before treatment, is improvedby treatment.

Materials treated-Cellulose-Paper Series F Examples 54-91 Table VI tofollow discloses the data obtained from a series F of Examples 54-88,Table VI discloses data from Examples 89-90, and Table VIII disclosesdata from an Example 911.

In Examples 54-91 the surfaces of a 5 mil thick Dryden kraft paper ofintermediate porosity were treated with CE; treatment gas at pressuresfrom 0.5 to 300 torr and with treatment times of 5 to 50 seconds for theexamples in Table VI and of seconds for the examples in Tables VII andVIII. It was noted that a well dried paper yields a significantly moreeflective treatment. The data indicate that pressures of CE, up to 300torr result in satisfactory treatment in the treatment time range of 25to 50 seconds at the power level used.

The data of Table VI also shows that satisfactory treatment may beobtained with shorter treatment if the power is raised sufficiently. Itcan be noted that Examples 64-68 demonstrate that with a pressure of 50torr and relative discharge power 1.0 (the absolute discharge powerbeing 0.2 kw./yd. that eifective treatment was not obtained withtreatment times less than 25 seconds. However, Examples 84-88 show thatincreasing the power provided eflective treatment with treatment timesas short as 3 seconds.

TABLE VI Water repellency Water drop test (control for untreatedsample=l3 seconds) Gas (Treatment times in seconds) press- Relative(Water drop test in hours) sure discharge Example number (torr) power 50sec. 25 sec. 12 sec. 6 sec. 3 sec.

1 No test made.

Since Tables II and III indicated that little gain was achieved byextending treatments beyond 100 seconds, the conditions of Examples59-63 (except for time) were repeated for 100 seconds as Examples 89 and90 and results are shown in the following Table VII.

Tables VI and VII therefore show by Examples 5490 of the presentinvention, that water repellency of kraft paper as measured by the Waterdrop test has been increased from a matter of 1 to 3 seconds, to amatter of several hours; and as measured by the static immersion test,the water repellency of kraft paper has been doubled.

Samples of the 5 mil thick Dryden kraft paper of intermediate porositywere treated using the gas CR Treatment time was 100 seconds and thedischarge power was 650 watts at a load voltage of 2.3 One-half inchstrips, eight inches in length, were cut from the treated paper and fromuntreated paper and the tensile strengths measured with an Instron ModelTT-C Universal Testing apparatus, in air, and with the use of auxiliaryliquid immersion test equipment, under a 6-l2 inch head of distilledwater. The results are given in Table VIII.

TABLE VIII Tensile strength in lbs. 1 in. (averaged) After under waterfor 30 Example Number In air seconds 91 10, 625 2, 900 Control 10, 460280 It is seen from the data in Table VIII that no significant change indry paper tensile strength has resulted from the treatment according tothis invention. However, upon comparison of the tensile strengthsmeasured under water it is shown that the treated samples retainapproximately one-third of their dry tensile strength while theuntreated control fell to a value of & of the average dry strength for anet gain in wet tensile strength of 10 for the treated paper.

Materials treated-polyethylene Series G Examples 92l05 tries of thepolyethylene coating is oxidative degradation (Underwater Degradation ofPolyethylene for Wire Insulation a paper presented by Yoshida, Tsunemi,Hasebe, Morikuni and Fukuda, Teruo at the Fifteenth Annual Wire andCable Symposium, Atlantic City, N.I., U.S.A., Dec. 8, 1966).

EXAMPLE 92 A 2 cm. long section of A I.D. O.D. polyethylene tubing wasplaced on the combination electrode/sample holder tube 36 in the cell 30(FIG. 3) and the cell evacuated via the outlet port 32. Helium gas wasintroduced into the cell 30 through port 31 at a constant slow flow rateand at a pressure of 0.12 torr. The two electrodes 35, 40 were connectedto the output terminals of a Cenco No. 80700 Tesla coil powered by aCenco No. 80365-3 high voltage transformer which in turn was energizedby a 60 Hz., 28 v. RMS source. The resulting discharge containing pulsesof up to 35 kv. was continued for a total of 8 minutes with the sampleholder 36 and sample 37 rotated one revolution during this time toinsure uniform exposure of the outer surface of the sample to thedischarge.

Following this pretreatment, the helium gas was turned oil and the CR;treatment gas introduced at a pressure of 0.5 torr and substantially thesame flow rate. A discharge of essentially the same characteristics wascarried out in the CR, environment for a total of 20 minutes with thesample holder 36 and sample 37 again rotated one revolution during thistime to assure uniform exposure of the sample surface.

After treatment the sample 37 was removed from the treatment cell andoven dried to constant weight, along with an untreated control and asimilar sample of the TABLE IX Weight loss after 6 hours immersion inchromic acid to 75 C.

A B C D E Treated polyethylene samples,

mg 2. 6 2. 6 2. 7 3. 7 2. 5 Control (untreated polyethylene), mg 19. 319. 4 20. 6 20. 7 22. 2 Teflon, mg. 0. 1

EXAMPLE 93 Two samples of tubing, as used in Example 92, were treated inthe manner described in Example 92 with the single exception that C Fwas substituted for CE; as the treatment gas to indicate the feasibilityof using other fluorocarbon gases. The following results were obtainedas set forth in Table X.

13 TABLE X Wt. loss after 6 hrs. immersion in chromic acid at 75 C., mg.

Treated polyethylene sample 5.7 Treated polyethylene sample 5.8 Control(untreated polyethylene) 18.3

EXAMPLE 94 Treated polyethylene sample.-. 3.1 mg. (total filmweight=60.8 mg). Control (untreated) 20.5 mg. (total filmweight=63.2mg.).

A series of three samples were treated, one repeating Example 92 and two(Examples 95 and 96) following the procedure of Example 92 but with thetime duration of the helium discharge varied, in each case the samplewas rotated one full revolution during the helium discharge. Thefollowing results shown in Table XII were obtained which indicates theadded desirability of pretreatment prior to the treatment in thefluorocarbon gas discharge:

TABLE XII Wt. loss due Helium to corrosion in discharge chromic acid,Example time, min. mg.

95 4 13. 5 (Example 92) 8 2. 5 96 16 2. 4

EXAMPLES 97-99 Three samples of polyethylene tubing as described inExample 92 were treated in accordance with the procedure of Example 92except that the helium pressure used during the helium discharge wasvaried. The following results shown in Table XIII were obtained whichshow that low pressure is required for the pretreatment step. The amountof weight loss due to corrosion is seen to increase sharply at thehighest of the three pretreatment pressures used.

TABLE XIII Helium Wt. loss discharge during pressure, chromic acidExample torr corrosion, mg.

EXAMPLES 100-102 Th'ree samples of polyethylene tubing were treated andtested according to the procedure described in Example 92 except thatthe time of exposure to the CE, discharge Cit 14 was varied. Thefollowing results shown in Table XIV were obtained showing the effect ofthe treatment time in the fluorocarbon gas discharge.

TABLE XIV Treatment Wt. less time to CF; during discharge, chromic acidExample min. corrosion, mg.

EXAMPLES |103-105 Three samples of polyethylene tubing were treated andtested in accordance with the procedures described in Ex ample 92 withthe exception that the pressure of the CE; gas during the discharge wasvaried. The following results shown in Table XV were obtainedillustrating the effect of Variation in the fluorocarbon gas pressure.

TABLE XV CF; Wt. loss discharge durlng pressure, chromic acid Exampletorr corrosion, mg.

MECHANISM OF THE INVENTION The mechanism operative in achieving thesurface changes described and illustrated in the examples which havebeen described is describable by a series of chemical steps initiated bythe discharge. Although it is not intended to restrict this patent bymechanism, it is felt that the consisency of the data with theexplanation of mechanism to follow together with the difference in kindof the changes which are observed to serve to describe the presentinvention as well as to distinguish it from the inventions and changesachieved in the processes of others, e.g., Wollinski and Coleman whichhave been discussed under the Description of the Prior Art.

The mechanism, in brief, visualized the activating of a gaseous speciescontaining a desired reactant, for example, the fluorine atom in thepresence of the surface with which it is to react. If the surface issufficiently reactive, the reaction is carried to the limits permittedby reaction equilibria and the surface properties desired.

For the special and somewhat unusual case of a relatively inert surfacesuch as polyethylene, pretreatment of the surface by discharge in heliumgas at a pressure low enough to permit efiective ion bombardment (andactivation of the surface) precedes treatment in the reactant gas. Thelow gas pressure requirement observed for pretreatment is believed toreflect the need for an average mean free path large enough to insureion energies capable of rupturing chemical bonds. Polyethylene may betaken as an example of an inert surface requiring both pretreatment andtreatment.

Pretreatment in helium at 0.1 torr (1) Discharge ionization of thehelium (2) Activation of the polyethylene sites by energetic helium ionsH x) m H Treatment in OR; at 5 torr (1) Discharge activation of CF or,ii on F (2) Reaction of discharge species with active polyethylene sitesTreatment in CR;

(1) Discharge activation of CR;

(2) Reaction of discharge species with active cellulose surface (9.) OHH (3) Addition of active gas species to the active surface sites 1 6TEST OF MECHANISM Saturation of treatment To distinguish betweenchemical reaction with the surface as illustrated in the above equationsand discharge initiated polymerization onto the surface, the followingexperiment was devised. A series of -80 weave cloth samples wereselected to be as uniform as possible and were discharge treated in CE;for varying lengths of time over a significantly wider range oftreatment time than was used in the treatment optimization study. Thesamples were then analyzed for fluoride content. If the pre vailingtreatment reaction is replacement of a surface atom by F or CFsaturation of the surface with F should be reached for the samplestreated for the excessive time periods and a plot of fluoride contentversus treatment time should fall off from a linear relationship.Converse- 1y, if polymerization occurs to any significant extent, nosaturation with treatment time should occur and the amount depositedshould be deposited linearly in time. Parameters such as discharge powerand gas pressure were maintained constant.

The results, FIG. 6, show the rate of the fluoride content addition tothe cotton samples to fall off rapidly after seconds of treatment andremain almost unchanged after 250 seconds indicating that deposition bypolymerization is very limited or completely absent.

Correlation between calculated fluoride content of saturated(perfluorinated) polyethylene surface and the fluoride found in analyzedsamples treated according to Example 94 Polyethylene films, 6 milsthick, and having macro surface areas of 4 square centimeters Weredischarge treated in CR, on both sides as described in Example 94 wereanalyzed for fluoride using a modification of the method of FluorineAnalysis which has been described. The' results, plotted in FIG. 5, showa fluoride content of the treated film to be linear in treated area.After correction for a low concentration of fluoride in the untreatedpolyethylene, discharge applied fluoride is calculated from FIG. 5 to be2.79 micrograms of fluoride per square centimeter of treated surface.

One can with the help of some simplifying assumptions calculate anapproximate number of replaceable surface hydrogen atoms on apolyethylene surface area for comparison with the observed fluorineatoms found per unit of macro area. If one assumes a polyethylenemicrosurface having an average of 1.25 angstrom (10- cm.) distancebetween carbon atoms, based on a 154x10 C-C bond distance and an averagebond angle of accessibility of treatment to all surface hydrogen atoms,and for simplicity, uniformity of carbon atom array in the surfaceplane, one can calculate the potentially replaceable hydrogen atoms asatoms/cm. of micro surface assuming two replaceable C-H bonds per carbonatom. An increase of a factor of two to three over this value calculatedfor a smooth surface can easily be expected depending on the ratio ofmicro to macro surface. The value observed 2.79 micrograms/cm. forfluorine content of the surface-treated films corresponds to a value of2.79 X 10-X 6 X 10 atoms/cmfi, 6 10 =atoms/mole and 19=grams/atom molefor fluorine, a value quite consistent with the value of 2.6 10atoms/cm. calculated from a model which assumed the replacement ofsurface H atoms by F atoms.

The assumptions made for the foregoing calculation were intentionallyand to a degree necessarily oversimplified. Assumptions of a flatsurface and of uniform CC bond distances in both directions in thesurface plane, for example, are oversimplified, but the errorsintroduced by their assumption would be compensatory and of the sameapproximate magnitude. Similarly, the assumptions of completeTeflonation, that is 100% conversion of all accessible G-H bonds to CFor CCF bonds and that only the surface is fluorinated lead to presumablysmaller and compensatory errors.

One can therefore expect to predict to within at least an order ofmagnitude the fluorine-content per square centimeter of treatedpolyethylene film and in particular should be able to differentiate asurface perfluorination reaction from a polymerization reaction onto thesurface. It has been here shown that the calculated value for Fatoms/cm. of surface is 2.6 which compares very well with the 8.8 10atoms/cm. found upon chemical analysis of a large group of the treatedfilms. The fact that the measured value is greater than the calculatedvalue is felt to reflect the oversimplified assumption of flat surface.In fact, the microsurface area is significantly larger than the assumedmacrosurface area due to the surface roughness.

By the foregoing description of apparatus, process steps and resultingmaterials of manufacture, it has been shown that by the presentinvention a treatment process has been found which increases thestability of polyethylene to oxidative attack. A 7-fold decrease inweight loss of treated samples was observed after 6 hours in chromicacid at 75 C. Weight loss of treated samples was 0.47 mg./crn. comparedto 3.4 mg./cm. for untreated polyethylene for comparable 6 hourexposures. It has also been by the foregoing description that thepresent invention is applicable to a wide range of natural and syntheticpolymers in woven or porous sheet form. As expected for the case ofperfluorination, increase in water repellency has been found to be ageneral property change. The water absorption of cotton cloth with anatural water absorption (ASTM D-583-63), of 57% has been reduced to-20%. Water absorption of wool cloth has been reduced from 58% to 22%.Treatment of nylon, which is already water repellent, decreased itswater absorption from 15% to 11%. Treatment of kraft paper resulted in areduction of its natural water absorption from 82% to 39% and anincrease in wet tensile strength from 280 lbs/in. to 3000 lbs./in.'-.

These observed desirable changes in properties have been related to theaddition of fluorine or fluorine-containing groups to the surfaces inquestion and new materials having the aforesaid desirablecharacteristics have been thereby created. Microchemical analysis ofpolyethylene film surfaces which had been discharge treated and shown topossess seven times the corrosion resistance of untreated films werefound to contain 2.79" micrograms of fluorine per cm. of surface.Similarly, analysis of treated 8'080 weave cotton cloth (waterabsorption: 29%) showed a fluorine content of 21.5 micrograms per squarecentimeter of macro surface. In general, fluorine content has been shownto be linear in discharge treatment time at short treatment times.

From the foregoing detailed description of the present invention, it hasbeen shown how the objects of the invention have been attained a variouspreferred manners. However, further modifications and equivalents of thedisclosed concepts such as readily occur to those skilled in the art areintended to be included within the scope of this invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A process for increasing the water repellency and wet strength ofkraft paper including the steps of: selecting a treatment gas from agroup consisting of CF C F C 1 C F CHF and SP arranging the paperbetween electrodes separated by an insulating material; flowing anatmosphere of the gas between the electrodes and in contact with thepaper at the rate of approximately 5 millimoles per minute under apressure of between 0.5 and 300 ton; and applying electric power to theelectrodes to expose a unit area of the paper to an electrodelessdischarge of electrical energy of about 0.2 k.w.h. per square yard ofpaper.

2. A process for increasing the water repellency and wet strength ofkraft paper including the steps of: selecting a treatment gas from agroup consisting of CF C F C F C F CHF and SP arranging the paperbetween electrodes separated by an insulating material; flowing anatmosphere of the gas between the electrodes and in contact with thepaper at the rate of approximately 5 millimoles per minute under apressure of between 0.5 and 300 torr; and applying electric power to theelectrodes to expose a unit area of the paper to an electrodelessdischarge of electrical energy of from between about 0.2 and 0.4 k.w.h.per square yard of paper.

References Cited UNITED STATES PATENTS 6/1966 Wolinski 11793.1 CD12/1968 Cofiman et a1. 11793.1 CD

US. Cl. X.R.

8120; 11747 A, 118, 138.8 B, 138.8 E, 142, 143 R, R; 204-16 5, 169

